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Outline for Octamethylcyclotetrasiloxane (D4) Peer Consultation

document, and Draft of Chapter 1

Purpose:  This document is a draft of the outline and Chapter 1 of the Risk Assessment Plan, which will

describe the approach that the U.S. Environmental Protection Agency (EPA) intends to use to perform a

nationally‐representative assessment of environmental risks associated with octamethylcyclotetrasiloxane

(D4).  The assessment should be sufficiently robust, and the uncertainties in the risk estimates sufficiently

characterized, to support risk management decisions should the assessment identify potential risks of

concern.  Therefore, this assessment is designed to include a quantitative assessment of the probable release

pathways of D4 to the environment that could contribute to a better understanding of the distribution of

concentrations, including high end concentrations, of D4 in environmental media at points of release. This

approach to identifying release pathways and environmental releases covers what are believed to be

representative industrial sources that have direct or indirect releases to the environment and down the drain

releases from commercial or consumer use of products containing D4. This approach will require the

collection of monitoring data on releases from industrial sites and waste water treatment plants, and

measured concentrations in environmental media and biota.

1. Background and Scope

A.   Introduction

This section will provide general information on use categories, production volume,

release sources and pathways, environmental fate, and hazard for D4.  

B.   Scope of Assessment for D4

This section will describe the ecological scenarios being considered, and the overall

approach for the workplan chemical risk assessment for D4.   

C.   Conceptual Model for Environmental Assessment of D4

This section will provide a schematic overview of the D4 ecological scenarios with a

depiction of release sources and environmental endpoints.  

2. Physical Chemistry and Environmental Fate  

A. Physical Chemical properties  

This section will provide information on the physical and chemical properties of D4.  The

EPA’s Enforceable Consent Agreement (ECA) process submissions, the Silicones

Environmental, Health and Safety Council of North America’s (SEHSC)’s data

submissions, and the peer‐reviewed literature will be among the data sources used.

B.   Environmental Fate  
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This section will provide information on environmental fate, including partitioning,

persistence in different media, and bioaccumulation in benthic and aquatic species.  The

EPA’s ECA process submissions, SEHSC’s data submissions, and the peer‐reviewed

literature will serve as the data sources.

   

3. Environmental Assessment  

   

A.  Environmental Release Assessment  

i. Lifecycle Description

This section will include a qualitative discussion of the manufacturing,

processing, and uses in the industrial, commercial, and consumer sectors.

Sources of information will include peer‐reviewed literature and

confidential industry submissions.

ii. Environmental  Release Assessment  

This section will include a description of EPA’s Office of Pollution Prevention

and Toxics (OPPT) plan for preparing a national release assessment of D4.  

Data will include peer‐reviewed literature and unpublished, non‐

confidential business submissions (CBI) will be used.  The various

approaches for developing the national release assessment will be

discussed, including the use of existing monitoring data.  Data gaps will be

identified, along with release estimation approaches and assumptions used

when data are lacking.       

B.  Environmental Exposure Assessment  

    i. Currently Available Monitoring Data

This section will review existing environmental monitoring data on cyclic

siloxanes, which were reported by various countries or SEHSC.

    ii. Monitoring Strategies Proposed

This section will cover the monitoring proposals submitted by SEHSC and by EPA

at the public ECA meetings.  For each monitoring proposal, a summary of 1) the

number of monitoring sites; 2) the number of direct versus indirect industrial

sites; 3) biota monitoring; and 4) the media to be collected at each site etc., will

be provided.  

C.  Environmental Hazard Assessment  
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This section will cover the hazard of D4 to the environment with available ecotoxicity

studies.   

D.  Environmental Risk Characterization   

This section will describe the approach that the Agency proposes to use to characterize

the potential risks of D4 to aquatic organisms, considering the SEHSC and Agency

monitoring proposals.  The risk characterization will be based on exposure and hazard

data.   

E.  Uncertainties/Data Gaps/Discussion

This section will describe the uncertainties, and data gaps associated with the risk

assessment approach for D4, based on the available data and information, and the

monitoring proposed by the SEHSC and the EPA.

4. References

This section will list references cited in the document.

5. Appendices    

This section will provide supplemental information.

DRAFT Chapter 1.  Background and Scope

A.  Introduction

The chemical Cyclotetrasiloxane, 2,2,4,4,6,6,8,8‐octamethyl‐ (D4, OMCTS; CASRN 556‐67‐2) was

identified for assessment as part of the United States (US) Environmental Protection Agency’s (EPA’s)

Existing Chemical Management Program

(http://www.epa.gov/oppt/existingchemicals/pubs/workplans.html).  The EPA plans to conduct a risk

assessment of D4. This document describes the risk assessment approach for D4 which will be reviewed

in a peer consultation.

D4 is a high production volume chemical that has a variety of industrial, commercial, and consumer

uses.  D4 is a cyclic siloxane mainly used as an intermediate for producing polydimethylsiloxane and

other silicone polymers, but it is also used directly in final goods and applications.  D4 is released to the

environment from a variety of different sources, including: manufacturing, processing, and formulating

sites, as well as both public and industrial wastewater treatment plants (WWTPs).  Consumer use of

products containing D4 also contributes to environmental loading.  D4 has been found in indoor air

[NYIEQ 2005], aquatic species [Kierkegaard 2011, Norden 2005, Powell 2008, SEHSC 2005], sediments

[Wang 2012], and wastewater treatment sludge [Norden 2005].  D4 is persistent in sediment,
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bioaccumulates in benthic and aquatic species, and is toxic to aquatic and sediment‐dwelling species

[Kierkegaard 2011, EC 2008, Springborn 1990].  To date, the only hazards of potential concern to

humans include reproductive (impaired fertility) and oncogenic effects (benign endometrial adenomas

of the uterus) observed in rodents (Siddiqui et al., 2007; Lee, 2004).  It has been suggested that the

mode of action for these effects may involve neuroendocrine mechanisms which are specific to rats

(Quinn et al., 2007a; Jean 2005); however, this has not been firmly established.  Human health will not

be the focus of this assessment.  

D4 has been the subject of regulatory activity in Canada and Norway.  Canada placed limits on the

percentage of D4 that can occur in consumer products and introduced a mandatory pollution prevention

program for processors and formulators (D4 is not manufactured in Canada).  Norway added D4 to its

list of priority substances, “Norway's national target is to eliminate or substantially reduce releases of

priority substances.”[Norden 2005, Kaj 2004, EC 2008]

In the United States, D4 is listed on the Toxic Substances Control Act (TSCA) inventory and is included in

the 2012 Chemical Data Reporting (CDR) Rule, but is not otherwise subject to specific TSCA regulations.

A memorandum of understanding (MOU) for hazard testing of the siloxanes was signed by EPA and Dow

Corning in 1996 to study a series of hazard endpoints. D4 is a component of personal care and consumer

products, including shampoo, sunscreen, and hair sprays. [EC 2008]

 D4 national production volume – 306 million pounds per year. D4 is also processed and

formulated into products in the USA for domestic use and export [EPA, 2012].

 D4 enters the environment through wastewater and sludge due to down‐the‐drain releases

from consumer products and releases at industrial sites. D4 is not readily biodegradable and

binds strongly to sediment, sludge and soil [EC 2008].

 D4 is highly persistent in sediment and highly bioaccumulative in benthic and aquatic organisms

[Xu 2009a, Xu 2009b, EC 2008].  The half‐life of D4 in air, water and soil is orders of magnitude

less than in sediment.  The degradation products of D4 in air, soil and water are not considered

to be toxic [SEHSC 2005b, EC 2008, Xu 2009a, Xu 2009b].

 The available toxicity data show that D4 is acutely toxic to fish and chronically toxic to aquatic

invertebrates [Sousa et al., 1995].  Two toxicity studies on blackworms (Lumbriculus variegates),

one in natural sediment [Picard, 2009a], and one in artificial sediment [Picard, 2009b] show that

D4 is toxic to sediment‐dwelling organisms.

 Monitoring Data for the U.S. are available for Lake Pepin in Minnesota and for publicly owned

treatment works (POTWs) in Oregon. Limited information is available for industrial releases and

for the resulting environmental levels.

 Limited biota monitoring data are available from Canada, Lake Pepin (Minnesota) and the

Norwegian environment, but do not adequately characterize benthic and aquatic concentrations

associated with U.S. manufacturing, processing or formulation [Powell 2010, Powell 2009,

Norden 2005].
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B.  Scope of Assessment for D4

Based on persistence, bioaccumulation, and acute and chronic toxicity to aquatic organisms, this

assessment will evaluate potential risk to the aquatic environment from the manufacturing, processing,

and formulating of D4, as well as from its commercial and consumer uses.  According to the reported

inventory update reporting rule (IUR) and CDR information, the majority of D4 is used as an

intermediate for producing silicone polymers with the remainder being used in a variety of consumer

products.  The use of products containing D4, such as personal care products, results in “down‐the‐

drain” releases into the wastewater stream.  D4 removal during treatment of municipal wastewater

influent is approximately 90%.  D4 is a high production volume chemical with a high acute toxicity for

aquatic organisms; therefore, EPA has concerns about the quantity of D4 released with the effluent

[Wang 2012].

Due to the lack of environmental monitoring data at industrial or commercial sites (including onsite

treatment systems) and the small amount of data at municipal WWTP sites in the United States, the EPA

entered into an ECA process with SEHSC to gather sufficient information to assess the pathways through

which D4 were entering the environment, and to determine the environmental levels at a

representative set of WWTPs to perform a national risk assessment for D4.  The available toxicity data

for D4 show that it is toxic to aquatic organisms.  The Agency recently placed D4 on the 2013‐2014

workplan chemical list.   

The workplan chemical risk assessment will focus on environmental endpoints.  The key questions that

need to be addressed include, but are not limited to:

1. What are the sources and pathways through which D4 enters the environment (e.g., manufacturing,

downstream processing and formulation, and end use)?

2. How do levels of D4 measured in surface water in the U.S. compare to levels that produce adverse

effects in aquatic organisms?

3. How do levels of D4 measured in sediment in the U.S. compare to levels that produce adverse effects

in sediment‐dwelling invertebrates?

4. How do biota concentrations near release sources (e.g., formulator sites) compare to previously

collected biota concentration data?  

C.   Conceptual Model for Environmental Assessment of D4

The scenarios evaluated for this assessment will be the release of D4 from the on‐site treatment

systems to POTW and to surface water, from the on‐site treatment systems to surface water, and from
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the POTW to surface water. The endpoints that will be evaluated for D4 ecological risk are acute and

chronic toxicity to aquatic and benthic organisms.  

The major exposure scenarios for D4 are depicted in the figure below.

Other

Processing

and

Formulating

sites

D4 Risk Assessment Conceptual Plan

Municipal

Wastewater Treatment Plant

* Cosmetics, sanitation goods, polishes, detergents, adhesives, sealants etc.

SEHSC

Manufacturing,

Processing,  

Formulating sites  

of D4

Effluent from Direct

Discharge Sites

Effluent from

Indirect

Discharge Sites

Down the drain

releases

On‐site Industrial

D4 Wastewater Treatment Plant Formulated

Product

Surface Water,

(Sediment,

Biota)

D4 product flow

Effluent flow

D4 enters the wastewater stream through down‐the‐drain releases from consumer products and from

releases at industrial sites (including processors and formulators).  Products that contain D4 are used

nationwide.  Studies have shown that D4 partitions to organic rich molecules and undergoes

evaporation; therefore, it is removed to a large extent during waste water treatment. [Wang 2012]

D4 is used as an intermediate for the production of silicone polymers and other commercial products.  

These facilities may have different release patterns, and EPA currently does not have adequate

information to assess the release fractions from these different processes.  Not all industrial sites are

required to report under the IUR/CDR rules, so EPA has limited information on the number or location of

the facilities or their release patterns.

Following release from WWTPs, D4 is expected to volatilize or to bind to organic content in the water or

sediment at the bottom of the water way.  Once in the sediment, D4 is highly persistent and has been

shown to bioaccumulate in benthic and aquatic species.   
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The proposed future D4 national risk assessment will use the data collected through the ECA to evaluate

potential environmental risks from D4, in addition to available monitoring data on D4. Furthermore,

estimates of environmental concentrations will be needed to supplement the measured concentrations,

to develop a national risk assessment of D4.  

References:

Dow Corning Corporation (DCC). 2008. 14C‐Octamethylcyclotetrasiloxane (14C‐D4): Prolonged toxicity

to the Rainbow trout (Oncorhynchus mykiss) under flow‐through test conditions.   DCC, Health and

Environmental Sciences, USA. DCC Report No. 2008‐10000‐59686. 2008‐11‐18.  

Environment Canada and Health Canada.  2008a.  Screening Assessment for the Challenge

Octamethylyclopentasiloxane (D4).  Available online from:

http://www.ec.gc.ca/substances/ese/eng/challenge/batch2/batch2_556‐67‐2.cfm as of May 3, 2010.

EPA 2012. Public Chemical Data Reporting (CDR) database.  Accessed March 8, 2013 at

http://java.epa.gov/oppt_chemical_search/

Kaj, L., Andersson, J., Palm‐Cousins, A., Remberger, M., Ekheden, Y., Dusan, B., Bror‐ström‐Lundén, E.

2005. Results from the Swedish National Screening Programme 2004: Subreport 4: Siloxanes. IVL.

Available from: www.imm.ki.se/Datavard/PDF/B1643_siloxaner.pdf

Kierkegaard, A.; van Egmond R.; McLachlan M.S.; Cyclic volatile methylsiloxane bioaccumulation in

flounder and ragworm in the Humber Estuary; Environ. Sci. Technol., 2011, 45 (14), pp 5936–5942; DOI:

10.1021/es200707r.  

Krueger et al. 2008; D4: A prolonged sediment toxicity test with Chironomus riparius using spiked

sediment. Wildlife International, Ltd. Project No. 570A‐107. DCC Report No. 2008‐10000‐59031.

[NYIEQ] New York Indoor Environmental Quality Center. 2005. Indoor Environmental Quality: Assessing

and Mitigating the Impact of Exposure to Multiple Indoor Contaminants. Project No. R828605‐01.  

Available from: www.syracusecoe.org/documents/2007/2/13/R828605‐01%20Final%20Report.pdf

Norden. 2005. Siloxanes in the Nordic Environment. TemaNord 2005:593. Copenhagen (NO), Nordic Council of

Ministers. Available from: http://www.norden.org/pub/miljo/miljo/uk/TN2005593.pdf

Picard 2009a. D4: A bioaccumulation test with Lumbriculus variegatus using spiked sediment. Wildlife

International, Ltd. Project No. 570A‐111.  DCC Report No. 2009‐I0000‐60372.

Picard 2009b. Octamethylcyclotetrasiloxane (D4): A prolonged sediment toxicity test with Lumbriculus

variegatus using spiked artificial sediment.   WI, Ltd., Maryland, USA. DCC Report No. 2009‐I0000‐60927.

WI Project Number: 570a‐110b.
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Powell DE. 2008. Interim update on cyclic methylsiloxane (cVMS) materials in surface sediment, cores,

and zooplankton for Lake Opeongo, Ontario, Canada. Centre Europeen des Silicones (CES). July 14, 2008.

[SEHSC] Silicones Environmental, Health and Safety Council. 2005. Degussa Corporation/Goldschmidt

GmbH: TSCA 8(e): Notification of Substantial Risk; Detection of Decamethylcyclopentasiloxane and

Octamethylcyclotetrasiloxane in the tissue of Fish from the Rhine River in Germany, October 10, 2005.

Data submitted to Environment Canada by the SEHSC, Herndon, VA, December 20, 2005. Environment

Canada submission # s70‐2006‐007.

Silicones Environmental, Health and Safety Council.  2005b.  Hydrolysis of Octamethylcyclotetrasiloxane

(D4).  SEHSC Technical Report No. 2863.  Herndon, VA.

Springborn Laboratories Inc.  1990.  Bioconcentration and elimination of c‐residues by fathead minnows

(Pimephales promelas) exposed to octamethylotetrasiloxane (final report) with cover letter dated

04/18/90.

Sousa, J.V., McNamara, P.C., Putt,A.E., Machado, M.W., Surprenant,D.C., Hamelink,J.L., Kent, D.J.,

Silberhorn, E.M.,  Hobson J.F. 1995. Effects of octamethylcyclotetrasiloxane (OMCTS) on freshwater and

marine organisms. Env. Toxicol. & Chemistry 14, 1639‐1647.

De‐Gao Wang, Helena Steer, Tara Tait, Zackery Williams, Grazina Pacepavicius, Teresa Young, Timothy

Ng, Shirley Anne Smyth, Laura Kinsman, Mehran Alaee, Concentrations of cyclic volatile methylsiloxanes

in biosolid amended soil, influent, effluent, receiving water, and sediment of wastewater treatment

plants in Canada, Chemosphere, Available online 21 November 2012, ISSN 0045‐6535,

10.1016/j.chemosphere.2012.10.047.

Xu, S. 2009a. Aerobic transformation of octamethylcyclotetrasiloxane (

14C ‐D4) in aquatic sediment

systems. HES Study 10885‐108 (MN4).

Xu, S. 2009b. Anaerobic transformation of octamethylcyclotetrasiloxane (

14C ‐D4) in aquatic sediment

systems. HES Study 11101‐108 (MN17a).